E. I. du Pont de Nemours and Company (DuPont) has been in the business of making Tyvek.RTM. spun bonded olefin sheet product for many years. However, the commercial process for making Tyvek.RTM. includes the use of a CFC (chlorofluorocarbon) spin agent. As the use of CFC's will soon be prohibited, DuPont has been developing a non-CFC process for manufacturing Tyvek.RTM. sheet. Unfortunately, there is, as yet, no identified spin agent that may be used as a simple substitute in place of the present CFC spin agent without requiring substantial modifications of the process or process conditions for manufacturing the product.
Thus, an entirely new facility has been built to manufacture Tyvek.RTM. sheet using a substantially modified process and a very different spin agent. The new spin agent is a hydrocarbon, namely: normal pentane, and just about every process activity and condition has been changed or scrutinized because the new spin agent does not act or react exactly like the CFC spin agent in the present commercial system. It is of course, the intent of all the developmental work to be able to produce essentially the same sheet product as made in the conventional commercial process so as to continue to develop the business and markets that the Tyvek.RTM. business has created.
The developmental work for recreating the process of making Tyvek.RTM. sheet has the additional object to form improved products that have better characteristics for current and new end uses.
It is a particular object of the present invention to provide sheet products that have a wider range of Gurley Hill Porosity Values than that which is attainable by conventional nonwoven technology.